Light emitting diode (LED) based lighting device arranged to emit a specific emission light following the Planckian locus in color space

Abstract

A light emitting diode (LED)-based lighting device is arranged to emit specific emission light that follows the Planckian locus in a color space, the LED-based lighting device comprising: a first LED channel comprising a plurality of LEDs, wherein the first LED channel is tuned to emit light having a first chromaticity in the color space; a second LED channel comprising a plurality of LEDs, wherein the second LED channel is tuned to emit light having a second chromaticity in the color space; a controller for activating the first and second LED channels so that the LED-based lighting device emits light having a color between the first and second chromaticities in the color space, wherein the LED-based lighting device further comprises a third LED channel connected between at least two of the LED channels, wherein the third LED channel comprises one or more LEDs, and wherein the third LED channel is tuned to emit light having a third chromaticity in the color space, wherein when the first channel is actuated, the third LED channel causes at least one LED of the second LED channel to be activated, thereby ensuring that the emitted light follows the Planckian locus in the color space between the first and second chromaticities in the color space.

Description

Technical Field

[0001] The present disclosure relates to a light emitting diode (LED) based lighting device arranged to emit light of a specific color, wherein the color of the light can be set using two color setting points, and wherein the color curve between those color setting points follows the Planckian locus. Background Art

[0002] Lighting devices utilizing light-emitting diodes (LEDs) have been developed for a variety of lighting applications. Due to their long lifespan and high energy efficiency, LED lamps are now also being designed to replace traditional fluorescent lamps, known as retrofit applications. For such applications, the retrofit LED lamp is typically adapted to fit into a socket in the corresponding lamp fixture being retrofitted. Furthermore, since lamp maintenance is typically performed by the user, the retrofit LED lamp should ideally be easy to operate with any type of suitable fixture, without requiring rewiring of the fixture.

[0003] The present disclosure relates to multi-channel (particularly dual-channel) LED-based lighting devices. Each channel can include multiple LEDs capable of emitting light of a specific color. For example, the first channel can be directed to emit red light. The second channel can be directed to emit green light, and the third channel can be directed to emit blue light.

[0004] In such lighting devices, a fixed voltage source can be used to power the LEDs in each channel. The current through each channel can be set at the factory by tuning a resistor placed in series with the LEDs in that particular channel. Among the disadvantages of this approach are several interfering factors, such as power supply voltage variations, cable length (i.e., impedance), and interactions between channels, which can lead to errors in the target flux and color point.

[0005] Another option is to use a current source to power the LEDs in each channel.The controller can activate the LED channels at a specific ratio to ensure that a specific emission light is emitted.

[0006] More specifically, a controller is typically used to control multiple switches, each of which is configured to enable a specific LED channel. For example, the first switch might enable the red channel, the second the green channel, the third the blue channel, and so on. A pulse-width modulated (PWM) signal with a specific duty cycle is supplied to the switches. The frequency of the PWM signal should be chosen so that it exceeds the refresh rate of the human eye. This prevents the user from perceiving flickering. By controlling the duty cycle, each channel's contribution to the total amount of light emitted can be controlled, and therefore, the color of the light emitted by the LED-based lighting device.

[0007] In current dual-channel LED-based lighting devices, the color point is tuned by changing the current ratio between the two channels. For example, one channel may have an LED arranged to emit light with a color temperature of 2700K, and the other channel may have an LED arranged to emit light with a color temperature of 6500K.

[0008] One of the drawbacks of the above-described dual-channel LED-based lighting device is that the color point of the emitted light of the LED-based lighting device can be tuned along a straight line in color space. This can lead to color perception issues, as the color may appear reddish, for example. Summary of the Invention

[0009] It would be advantageous to have a lighting device based on light emitting diodes (LEDs) arranged for emitting a specific emission light that follows the Planckian locus in color space.

[0010] In a first aspect, a light emitting diode (LED)-based lighting device is provided, which is arranged to emit a specific emission light that follows the Planckian locus in a color space. The LED-based lighting device comprises:

[0011] - a first LED channel comprising at least one LED, wherein the first LED channel is tuned to emit light having a first chromaticity in a color space;

[0012] - a second LED channel comprising at least one LED, wherein the second LED channel is tuned to emit light having a second chromaticity in the color space;

[0013] - a controller for activating the first LED channel and the second LED channel so that the LED-based lighting device emits light having a color between a first chromaticity and a second chromaticity in a color space;

[0014] LED-based lighting equipment also includes:

[0015] a third LED channel connected between an input of the first LED channel and an input of the second LED channel, wherein the third LED channel comprises at least one LED, and wherein the third LED channel is tuned to emit light having a third chromaticity in a color space, wherein when the first channel is actuated, the third LED channel causes the at least one LED of the second LED channel to be activated.

[0016] Therefore, light can be represented by a color point (x1, y1) in the color space.

[0017] According to the present disclosure, the Planckian locus or blackbody locus is the path or locus that the color of an incandescent blackbody will occupy in a particular chromaticity space as the blackbody temperature changes. It goes from deep red at low temperatures through orange, yellow-white, white, and finally to bluish-white at very high temperatures.

[0018] The inventors have discovered that when the emitted light follows the Planckian locus in color space, users can perceive natural color transitions. In the prior art, the color transition between two LED channels is displayed as a straight line in color space between the set points of the two LED channels. This can be perceived as undesirable.

[0019] According to the present disclosure, color space can be viewed as a three-dimensional space. That is, color can be specified by a set of three numbers, such as CIE coordinates X, Y, and Z, or other values ​​such as hue, colorfulness, and brightness, which specify the color and brightness of a particular uniform visual stimulus.

[0020] Chromaticity is the projection of color onto a two-dimensional space that ignores brightness. For example, the standard CIE XYZ color space projects directly onto a corresponding chromaticity space specified by two chromaticity coordinates called x and y, forming the CIE chromaticity diagram.

[0021] According to the present disclosure, chromaticity is an objective specification of the quality of a color, regardless of its brightness. Chromaticity can be composed of two independent parameters, designated, for example, as hue and chromaticity, the latter of which can alternatively be referred to as saturation, chroma, intensity, or excitation purity. This quantity is derived from the trichromatic color vision of most humans, which is adopted by most models in color science.

[0022] From the above, the inventors have the insight that a controller should be able to control the channels in such a way that the color emitted by the LED-based lighting device follows the Planckian locus in color space.

[0023] Note that the present disclosure utilizes the forward voltage-current characteristic of LEDs for introducing nonlinearity. This concept is better explained here in more detail below.

[0024] It should also be noted that using the concepts of the present disclosure, the resulting line in color space may not follow the Planckian locus exactly, but may match the Planckian locus better than a conventional straight line.

[0025] In one example, the sum of the forward voltage of the second LED channel and the forward voltage of the third LED channel is equal to the forward voltage of the first LED channel. This provides optimal control of the current distribution among the three LED channels.

[0026] In one example, the first LED channel includes a plurality of LEDs, and wherein the second LED channel includes a plurality of LEDs, and the third LED channel is connected between the plurality of LEDs of the first LED channel at a first end and is connected between the plurality of LEDs of the second LED channel at a second end opposite the first end.

[0027] One purpose of the above example is to introduce nonlinearity when activating the first LED channel. The current flowing through the first LED channel will also flow through a portion of the second LED channel via the third LED channel. Thus, the LED current can be split into two currents. The first current can continue to flow through the remaining LEDs in the first LED channel, while the second current can flow to the second LED channel via the third LED channel and can flow through one or more LEDs in the second LED channel.

[0028] In another example, the number of LEDs in the first channel cascaded in series with their anode sides connected to the first end of the third LED channel is equal to the number of LEDs connected in series in the third LED channel plus the number of LEDs in the second LED channel connected in series with their anode sides connected to the second end of the third LED channel.

[0029] It has been found that it may be beneficial to ensure that the total number of LEDs through which the first current flows is equal to the total number of LEDs through which the second current flows.

[0030] In another example:

[0031] - A first LED channel includes five initial LEDs followed by ten subsequent LEDs;

[0032] - The second LED channel consists of five initial LEDs followed by five subsequent LEDs,

[0033] A third LED channel includes five LEDs, wherein a first end of the third LED channel is connected between an initial LED and a subsequent LED of the first LED channel, and wherein a second end of the third LED channel is connected between an initial LED and a subsequent LED of the second LED channel.

[0034] The above examples are practical implementations of LED-based lighting devices.

[0035] The controller may, for example, activate the second LED channel. In this case, current will flow through the first five LEDs of the second LED channel and then through the five subsequent LEDs.

[0036] For example, the controller can also activate the first LED channel. In this case, current will flow through the first five LEDs of the first LED channel. Then, current will flow through the five subsequent LEDs of the first LED channel, or through the LEDs of the third LED channel and the five subsequent LEDs of the second channel, or a combination thereof. This also depends on the amount of current flowing through the second LED channel.

[0037] This is best explained as follows. The voltage across a particular LED also depends on the current flowing through that LED. Thus, the present disclosure exploits the concept that the forward voltage of an LED also depends on the current flowing through the corresponding LED.

[0038] If the current through the second LED channel is relatively large, no current will flow through the third LED channel. This means that the voltage at the second end of the third LED channel is increased due to the sum of the forward voltages of the subsequent LEDs in the second LED channel. Consequently, the voltage across the LEDs in the third LED channel may not be sufficient to allow current to flow through those LEDs.

[0039] Thus, the above relates to the non-linearity introduced by the present disclosure.In other words, given a certain total current ratio between the first LED channel and the second LED channel, current will flow from the first LED channel to the second LED channel via the third LED channel.

[0040] In another example, the color temperature of the first chromaticity is lower than the color temperature of the second chromaticity.

[0041] In yet another example, a lighting device has two LED channels.

[0042] In yet another example, the first LED channel is arranged to emit light having a temperature of 2700K, and wherein the second LED channel is arranged to emit light having a temperature of 6500K.

[0043] Note that the controller can be either a pulse-width modulation (PWM)-based controller or a linearly operated controller. A PWM-based controller means that the controller can control switches present in a channel to activate the corresponding channel using a PWM control signal. This means that a particular LED channel is either on or off. A linearly operated controller can control each LED channel by providing a linear controller current through the corresponding LED channel. As such, the amount of current through the LED channel may not be fixed, but may vary depending on the controller's settings.

[0044] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A light emitting diode (LED) based lighting device with two LED channels according to the prior art is shown;

[0046] Figure 2 An LED-based lighting device having two LED channels according to the present disclosure is shown;

[0047] Figure 3 shows another LED-based lighting device having two LED channels according to the present disclosure;

[0048] Figure 4 A chromaticity diagram illustrating the concept of the Planckian locus is shown;

[0049] Figure 5 One example of a graph illustrating flux ratio versus current ratio according to the present disclosure is shown. DETAILED DESCRIPTION

[0050] Figure 1 A lighting device 1 based on light emitting diodes (LEDs) with two LED channels according to the prior art is shown.

[0051] An LED-based lighting device 1 includes a driver configured to drive two different channels 2 and 3. The first LED channel 2 can be configured to emit a color having a temperature of 2700 Kelvin, also known as warm white. The second LED channel can be configured to emit a color having a temperature of 6500 Kelvin, also known as daylight white. By combining these two channels, a color between warm white and daylight white can be achieved.

[0052] The LED based lighting device 1 has a single return line, as indicated with reference numeral 4. This return line is used for any current originating from the first 2 and second 3 LED channels.

[0053] Figure 2 An LED-based lighting device 11 having two LED channels according to the present disclosure is shown.

[0054] LED-based lighting device 11 has two channels, as indicated by the terms "Channel 1" and "Channel 2." First channel 12 may have at least one LED tuned to emit light having a first chromaticity. Second channel 13 may have at least one LED tuned to emit light having a second chromaticity. Light-emitting diode (LED)-based lighting device 11 is configured to emit specific light emission that follows the Planckian locus in a color space. More specifically, first channel 12 may be configured to emit a color having a temperature of 2700K, and second channel 13 may be configured to emit a color having a temperature of 6500K. LED-based lighting device 11 includes a third LED channel 14 connected between the input of first LED channel 12 and the input of second LED channel 13. Third LED channel 14 has at least one LED tuned to emit light having a third chromaticity in the color space. When the first channel is activated, third LED channel 14 causes at least one LED of second LED channel 13 to activate. The third LED channel 14 may emit light having a reddish color to create a warmer effect in the overall light output of the LED-based lighting device 11 .

[0055] The LED based lighting device 11 herein is arranged to emit a specific emission light that follows the Planckian locus in color space.

[0056] In physics and color science, the Planck locus or blackbody locus is the path or trajectory that the color of an incandescent black body will take in a particular color space (i.e., chromaticity space) as the blackbody's temperature changes. It goes from deep red at low temperatures through orange, yellow-white, white, and finally to bluish-white at very high temperatures.

[0057] According to the present disclosure, a color space is a three-dimensional space. That is, a particular color can be specified by a set of three numbers, such as CIE coordinates X, Y, and Z, or other values ​​such as hue, colorfulness, and brightness.

[0058] The present disclosure is not limited to the manner in which these three numbers are composed.

[0059] Chromaticity is the projection of color into a two-dimensional space that ignores brightness. For example, the standard CIE XYZ color space is directly projected onto a corresponding chromaticity space specified by two chromaticity coordinates called x and y, forming Figure 4 The familiar chromaticity diagram is shown in .

[0060] The Planckian locus (the path that the color of a black body takes as its temperature changes) is usually shown in this standard color space, which is about Figure 4 Explained in more detail: Preferably, the sum of the forward voltage of the second LED channel and the forward voltage of the third LED channel is equal to the forward voltage of the first LED channel.

[0061] exist Figure 3 , another LED-based lighting device 11 according to the present invention is described having two LED channels. The first LED channel 12 includes a plurality of initial LEDs followed by a plurality of subsequent LEDs. In this particular example, five initial LEDs are shown, as indicated by the reference numeral "#5," and ten subsequent LEDs are shown, as indicated by the reference numeral "#10."

[0062] The initial LED and subsequent LEDs may be of the same type. That is, each LED may be arranged to emit a color having a temperature of 2700K.

[0063] The second LED channel 13 comprises a plurality of initial LEDs followed by a plurality of subsequent LEDs. In this particular example, ten initial LEDs are shown, as indicated by reference numeral "#10", and five subsequent LEDs are shown, as indicated by reference numeral "#5".

[0064] The LED-based lighting device 11 includes a third LED channel 14 connected between at least two LED channels, wherein the third LED channel 14 includes one or more LEDs, and wherein the third LED channel 14 is tuned to emit light having a third chromaticity in a color space, wherein when the first channel 12 is actuated, the third LED channel 14 causes at least one LED of the second LED channel 13 to be activated, thereby ensuring that the emitted light follows the Planckian locus in the color space between the first and second chromaticities in the color space.

[0065] In this particular case, the third LED channel 14 includes five LEDs as indicated by reference number “#5,” wherein a first end of the third LED channel 14 is connected between an initial LED and subsequent LEDs of the first LED channel 12, and wherein a second end of the third LED channel 14 is connected between an initial LED and subsequent LEDs of the second LED channel 13.

[0066] Figure 4 A chromaticity diagram 51 illustrating the concept of the Planckian locus is shown.

[0067] Here, reference numeral 51 indicates a point in the chromaticity diagram associated with the second LED channel 13, and reference numeral 52 indicates a point in the chromaticity diagram associated with the first LED channel 12. Figure 1 In the described prior art case, LED channels can be combined so that the color emitted by the LED-based lighting device follows a straight line 54 between two points 51 , 52 .

[0068] The LED based lighting device according to the present disclosure is arranged to follow the Planckian locus between two points 51 , 52 , as indicated with reference numeral 53 .

[0069] Figure 5 One example of a graph 61 illustrating flux ratio versus current ratio according to the present disclosure is shown.

[0070] Reference numeral 62 indicates a ratio of fluxes originating from the second LED channel 13 , reference numeral 63 indicates a ratio of fluxes originating from the first LED channel 12 , and reference numeral 64 indicates a ratio of fluxes originating from the third LED channel 14 .

[0071] As shown in the figure, the third LED channel 14 only starts to function once a certain current ratio occurs between the first LED channel 12 and the second LED channel 13. That is, if a small amount of current flows through the first LED channel 12, then that amount of current may not flow through the third LED channel 14. This is explained as follows.

[0072] The large current flowing through the second LED channel 13 causes the potential at the cathode side of the third LED channel 14 to increase due to the forward voltage of the subsequent LEDs of the second LED channel 13. This will result in the effect that the voltage across the third LED channel 14 is too low to cause the LEDs in the third LED channel 14 to start conducting.

[0073] Once the ratio between the currents through the first LED channel 12 and the second LED channel 13 reaches a certain threshold, the LEDs in the third LED channel 14 will begin conducting current. This is shown at approximately the 35% mark on the horizontal axis. In this case, the voltage of the third LED channel 14 has just exceeded the threshold voltage, causing the LEDs in the third LED channel 14 to begin conducting current. The current injected into the first LED channel 12 is then split between the current through the third LED channel 14 and the current through the subsequent LEDs in the first LED channel 12. This is shown in the figure by the nod in the flux originating from the first LED channel 12 at approximately 35% on the horizontal axis.

[0074] Thus, as indicated above, the current through the first LED channel 12 does not immediately split itself, allowing current to flow through the third LED channel 14. The third LED channel 14 only begins to function once a certain current ratio between the first LED channel 12 and the second LED channel 13 is achieved. That is, the third LED channel 14 begins conducting current when the ratio between the current through the first LED channel 12 and the current through the second LED channel 13 is above a predetermined threshold. This results in a desirable nonlinearity because it causes the color to more closely follow the Planckian locus.

[0075] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit can perform the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not mean that a combination of these measures cannot be used to advantage. The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium supplied together with or as part of other hardware, but the computer program may also be distributed in other forms, for example via the Internet or other wired or wireless telecommunications systems. Any reference signs in the claims should not be construed as limiting their scope.

Claims

1. A lighting device (11) based on a light emitting diode (LED), said LED based lighting device being arranged for emitting a specific emission light following a Planckian locus in a color space, wherein said LED based lighting device (11) comprises: - a driver arranged to drive the first channel and the second channel; a first LED channel (12) adapted to receive current from the first channel and comprising at least one LED, wherein the first LED channel (12) is tuned to emit light having a first chromaticity in the color space; a second LED channel (13) adapted to receive current from the second channel and comprising at least one LED, wherein the second LED channel (13) is tuned to emit light having a second chromaticity in the color space; - a controller adapted to activate the first channel and the second channel such that the LED-based lighting device (11) emits light having a color between the first chromaticity and the second chromaticity in the color space; The LED-based lighting device (11) further comprises: a third LED channel (14) connected between an input of the first LED channel (12) and an input of the second LED channel (13), wherein the third LED channel (14) comprises at least one LED, and wherein the third LED channel (14) is tuned to emit light having a third chromaticity in the color space, wherein when the first LED channel (12) is activated, the third LED channel (14) causes the at least one LED of the second LED channel (13) to be activated. 2 . The LED-based lighting device of claim 1 , wherein a sum of a forward voltage of the second LED channel and a forward voltage of the third LED channel is equal to a forward voltage of the first LED channel.

3. The LED-based lighting device of claim 1 , wherein the first LED channel comprises a plurality of LEDs, and wherein the second LED channel comprises a plurality of LEDs, an anode of a first LED of the first plurality of LEDs is connected to a first output terminal of the driver, an anode of a first LED of the second plurality of LEDs is connected to a second output terminal of the driver different from the first output terminal, and a cathode of a last LED of the first plurality of LEDs and a cathode of a last LED of the second plurality of LEDs are connected to a third terminal of the driver, and wherein the third LED channel is connected between the plurality of LEDs of the first LED channel at a first end and is connected between the plurality of LEDs of the second LED channel at a second end opposite the first end.

4. The LED-based lighting device of claim 3 , wherein the number of series-connected LEDs in the first LED channel connected with their anode sides to the first end of the third LED channel is equal to the number of series-connected LEDs in the third LED channel plus the number of series-connected LEDs in the second LED channel connected with their anode sides to the second end of the third LED channel.

5. The LED-based lighting device of claim 4, wherein: - the first LED channel comprises five initial LEDs followed by ten subsequent LEDs; - the second LED channel comprises five initial LEDs followed by five subsequent LEDs, The third LED channel includes five LEDs, wherein the first end of the third LED channel is connected between the initial LED and the subsequent LEDs of the first LED channel, and wherein the second end of the third LED channel is connected between the initial LED and the subsequent LEDs of the second LED channel.

6. The LED-based lighting device of any one of claims 1, 2, 4, and 5, wherein the color temperature of the first chromaticity is lower than the color temperature of the second chromaticity.

7. The LED-based lighting device of any one of claims 1, 2, 4, and 5, wherein the first LED channel is arranged to emit light having a temperature of 2700K, and wherein the second LED channel is arranged to emit light having a temperature of 6500K.

8. The LED-based lighting device of any one of claims 1, 2, 4, and 5, wherein the controller is any of the following: - a controller based on pulse width modulation (PWM), or - Controller for linear operation.

9. The LED-based lighting device of claim 8, wherein the controller is arranged to provide a first current to the first LED channel and a second current to the second LED channel.

10. The LED-based lighting device of any one of claims 1, 2, 4, 5, and 9, wherein the controller activates the first channel and the second channel to change the ratio between the current through the first LED channel (12) and the current through the second LED channel (13).

11. The LED-based lighting device of claim 9 , wherein the controller is a linearly operated controller that controls each of the first LED channel ( 12 ) and the second LED channel ( 13 ) by providing a linear controller current through the corresponding LED channel, such that the amount of current through the first LED channel ( 12 ) and / or the amount of current through the second LED channel ( 13 ) varies depending on a setting of the controller.

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